This invention relates to a method of crystallizing an aluminophosphate molecular sieve within particles. Molecular sieves belong to a commercially important class of crystalline materials. They have distinct crystal frameworks with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species. Natural and synthetic crystalline molecular sieves are useful as catalysts and adsorbents. The adsorptive and catalytic properties of each molecular sieve are determined in part by the dimensions of its pores and cavities. Thus, the utility of a particular molecular sieve in a particular application depends at least partly on its crystal structure. Because of their unique sieving characteristics, as well as their catalytic properties, molecular sieves are especially useful in such applications as gas drying and separation and hydrocarbon conversion. The term "molecular sieve" refers to a material prepared according to the present invention having a fixed, open-network structure, usually crystalline, that may be used to separate hydrocarbons or other mixtures by selective occlusion of one or more of the constituents, or may be used as a catalyst in a catalytic conversion process.
The molecular sieve prepared according to the present method belongs to the family of crystalline aluminophosphates comprising AlO.sub.2 ! and PO.sub.2 ! oxide units in tetrahedral coordination which possess physical and chemical properties as molecular sieves. In addition to the AlO.sub.2 ! and PO.sub.2 ! oxide units described above, the molecular sieve of the present process may also contain one or more optional elements other than alumina and phosphorous, where each optional element is also capable of forming oxide units in the crystalline framework of the aluminophosphate.
The method of this invention is also directed to a process for preparing a class of molecular sieves known as non-zeolitic molecular sieves, as defined in U.S. Pat. No. 4,913,799, the disclosure of which, and in particular that disclosure relating to the description of specific non-zeolitic molecular sieves and to their preparation, is incorporated herein by reference. As used herein, the term "non-zeolitic molecular sieve" and its abbreviation "NZMS" will be used interchangeably.
Non-zeolitic molecular sieves are conventionally prepared by crystallization from liquid solutions. Conventional methods for preparing aluminophosphate-containing molecular sieves are taught, for example, in U.S. Pat. Nos. 4,310,440; 4,440,871; 4,567,029; 4,686,093; 4,913,799 and 4,973,785. Crystallizing a non-zeolitic molecular sieve from such a liquid solution typically produces finely divided crystals which must be separated from the liquid in which the molecular sieve is crystallized. The separated liquid, in turn, contains substantial concentrations of dissolved reactants, and must be treated for reuse or else be discarded, with potentially deleterious environmental consequences. The dissolved reactants also pose a significant cost for recovery or disposal. Preparing commercially useful catalytic materials using the conventionally prepared molecular sieve also normally requires additional binding and forming steps. Typically, the molecular sieve powder as conventionally prepared must be mixed with a binder material and then formed into shaped particles, using methods such as extrusion. These binding and forming steps greatly increase the complexity of preparing the non-zeolitic molecular sieve as a catalyst. The additional steps may also have an adverse effect on the catalytic performance of the molecular sieve so bound and formed.
The process of the present invention for preparing a non-zeolitic molecular sieve, which process overcomes the inefficiencies of the multiple step conventional preparation process, provides a method for forming the molecular sieve crystals within particles.